Compositions, devices and methods for hydrogen generation

ABSTRACT

Methods and systems for hydrogen generation from solid hydrogen storage compositions which generate hydrogen in an exothermic reaction wherein the heat released can be absorbed by solid endothermic compositions are disclosed. The solid hydrogen storage compositions comprise mixtures of chemical hydrides and water surrogate compounds. Fuel cartridges suitable for use with compositions which generate hydrogen upon the application of thermal initiation and methods for operating the fuel cartridges are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/907,232, filed Mar. 26, 2007, the entire disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to hydrogen storage compositions andmethods for thermally initiating hydrogen generation from hydrogenstorage compositions.

BACKGROUND OF THE INVENTION

There is an ongoing need for new energy and power sources to meet thegrowing demand for portable power. Fuel cells are being considered asreplacements for batteries. A fuel cell for small applications needs tobe compact, lightweight, and have a high energy storage density.

Hydrogen is the fuel of choice for fuel cells. Their adoption isdependent on finding a convenient and safe hydrogen source due todifficulties in storing the gas. Various non-gaseous hydrogen carriers,including hydrocarbons, metal hydrides, and chemical hydrides are beingconsidered as hydrogen storage and supply systems. In each case, systemsneed to be developed to release the hydrogen from its carrier, either byreformation as in the case of hydrocarbons, desorption from metalhydrides, or catalyzed hydrolysis of chemical hydrides.

There is a need for hydrogen generation systems that are compact andthat minimize the presence of gaseous hydrogen while providing favorablehydrogen storage metrics. Hydrogen generation systems, wherein operatingdemands of the fuel cell are matched to control of the flow rate andpressure of the system, are also needed.

BRIEF SUMMARY OF THE INVENTION

The invention provides systems and heat-activated methods of hydrogengeneration in which the generation of hydrogen is initiated by theapplication of heat to hydrogen storage compositions. The presentinvention also provides fuel cartridges suitable for use with thecompositions and methods disclosed herein. The methods provide hydrogengeneration systems that minimize the presence of gaseous hydrogen byproducing hydrogen on an as-needed basis.

BRIEF DESCRIPTION OF THE DRAWINGS

A complete understanding of the invention may be obtained by referenceto the accompanying drawings when considered in conjunction with thefollowing detailed description, in which:

FIG. 1 is a cross sectional view of an exemplary fuel cartridge usefulin embodiments of the invention.

FIGS. 2A, 2B, and 2C are cross sectional views of fuel compartmentarrangements in accordance with embodiments of the invention.

FIGS. 3A and 3B illustrate alternate configurations of exothermic andendothermic compositions in accordance with embodiments of theinvention.

FIG. 4 is a cross sectional view of a multiple layer arrangement of fuelcompartments in accordance with an embodiment of the invention.

FIG. 5 is a diagram of an arrangement of fuel compartments in accordancewith an embodiment of the invention.

FIG. 6 is a diagram of an arrangement of fuel compartments in accordancewith an embodiment of the invention.

FIG. 7 is a diagram of an arrangement of fuel compartments in accordancewith an embodiment of the invention.

FIGS. 8A, 8B, and 8C illustrate arrangements of initiation elementsuseful in embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides methods for thermally initiated hydrogengeneration from solid exothermic hydrogen storage compositions whereinthe heat released can be absorbed by solid endothermic compositions. Theinvention further provides methods for thermally initiated hydrogengeneration from solid hydrogen storage compositions wherein hydrogen isgenerated in an exothermic reaction and the heat released can be used toinitiate hydrogen generation from solid hydrogen storage compositions inan endothermic reaction. The invention also provides reactors for thegeneration of hydrogen, wherein at least one exothermic hydrogengeneration reaction is coupled to at least one endothermic hydrogengeneration reaction, and fuel cartridges suitable for use with thereactors and methods disclosed herein. The reactors and processes of thepresent invention provide passive hydrogen generation systems withminimal system complexity. By coupling heat-absorbing and heat-releasingmaterials together, the hydrogen generating materials within a storagecartridge can be packaged efficiently and safely.

One embodiment of the invention provides a process for generatinghydrogen comprising: providing at least one solid fuel composition whichgenerates hydrogen in an exothermic reaction, and providing at least onehydrogen generation composition which generates hydrogen in anendothermic reaction; using thermal initiation to generate hydrogen andheat from the exothermic solid fuel composition; and using the heat togenerate hydrogen from the endothermic hydrogen generation composition.

Another embodiment of the invention provides a process for generatinghydrogen comprising: providing at least one solid fuel composition whichgenerates hydrogen in an exothermic reaction, and providing at least onegas generation composition which generates a gas in an endothermicreaction; using thermal initiation to generate hydrogen and heat fromthe exothermic solid fuel composition; and using the heat to generate agas from the endothermic gas generation composition.

In another embodiment, the invention provides a fuel cartridge thatprovides hydrogen for conversion to energy by a power module comprisinga fuel cell or hydrogen-burning engine, or to a hydrogen storage devicesuch as a hydrogen cylinder, a metal hydride, or a balloon. The fuelcartridge comprises a housing containing a plurality of fuelcompartments separated from one another, and at least one initiationelement in communication with at least one fuel compartment containingat least one solid fuel composition which generates hydrogen in anexothermic reaction, and at least one fuel compartment containing atleast one gas generation composition which generates a gas in anendothermic reaction.

In another embodiment, the invention provides a fuel cartridge thatprovides hydrogen for conversion to energy by a power module comprisinga fuel cell or hydrogen-burning engine, or to a hydrogen storage devicesuch as a hydrogen cylinder, a metal hydride, or a balloon. The fuelcartridge comprises a housing containing a plurality of fuelcompartments separated from one another by porous walls, and at leastone initiation element in communication with at least one fuelcompartment containing at least one solid fuel composition whichgenerates hydrogen in an exothermic reaction, and at least one fuelcompartment containing at least one gas generation composition whichgenerates a gas in an endothermic reaction.

In another embodiment, the invention provides a fuel cartridge thatprovides hydrogen for conversion to energy by a power module comprisinga fuel cell or hydrogen-burning engine or to a hydrogen storage devicesuch as a hydrogen cylinder, a metal hydride, or a balloon. The fuelcartridge comprises a housing containing a plurality of fuelcompartments separated from one another by porous walls, wherein eachfuel compartment contains at least one solid fuel composition whichgenerates hydrogen in an exothermic reaction and at least one gasgeneration composition which generates a gas in an endothermic reaction,and at least one initiation element in communication with at least onesolid fuel composition which generates hydrogen in an exothermicreaction.

In another embodiment, the invention provides a fuel cartridge thatprovides hydrogen to a power module comprising a fuel cell orhydrogen-burning engine for conversion to energy, or to a hydrogenstorage device such as a hydrogen cylinder, a metal hydride, or aballoon. The fuel cartridge comprises a housing containing a pluralityof fuel compartments separated from one another by porous walls, whereineach fuel compartment contains at least one solid fuel composition whichgenerates hydrogen in an exothermic reaction and at least one gasgeneration composition which generates a gas in an endothermic reactionseparated from each other by a porous spacer, and at least oneinitiation element in communication with at least one solid fuelcomposition which generates hydrogen in an exothermic reaction.

The methods and reactors of the present invention can be operated toproduce hydrogen in an as-needed mode in which hydrogen is consumed orutilized immediately or on an on-going basis. Alternatively, the methodsand reactors can be used in a batch mode in which hydrogen is generatedand stored in a ballast region until required by the hydrogen consumingdevice.

The term “solid,” as used herein encompasses any nongaseous andnonliquid form, including powders, caplets, tablets, pellets, granules,rods, fibers, crystals, and monoliths, for example.

As used herein, the term “exothermic” means that heat is released whenhydrogen is produced. Exothermic hydrogen generation storagecompositions useful in embodiments of the invention preferably includemixtures of at least one chemical hydride compound and at least one“water surrogate” source. The water surrogate/chemical hydridecompositions are preferably solid. The individual components may bephysically mixed together, or may be combined into a pellet, caplet, ortablet comprising at least two components. Hydrogen is generated whenheat is applied to the exothermic hydrogen generation storagecomposition either by heating a reactor containing the materials or byan initiation element that is in contact with the hydrogen storagecompositions. Heat need only be applied to initiate hydrogen generation.Once initiated, the hydrogen generation reaction is self-sustaining andthe hydrogen storage composition need not be heated continuously duringthe reaction. Preferably, the hydrogen generation reaction is initiatedat a temperature (i.e., the “onset temperature”) between about 313 K toabout 773 K, preferably between about 333 K to about 523 K, morepreferably between about 373 K to about 473 K, and most preferablybetween about 393 K to about 453 K. As used herein, the term “about” isheld to mean within 10% of the stated value.

Suitable chemical hydrides include, but are not limited to, boronhydrides, ionic hydride salts, and aluminum hydrides. These chemicalhydrides may be utilized in mixtures or individually. The hydrogen atomscontained within the chemical hydrides are referred to herein as“hydridic hydrogens,” and can be represented as “H”. A hydridic hydrogenis a hydrogen atom bound to an element less electronegative thanhydrogen on the Pauling scale or is bound to Ru, Rh, Pd, Os, Ir, Pt, Au,or As.

As used herein, the term “boron hydrides” includes boranes, polyhedralboranes, and anions of borohydrides or polyhedral boranes. Suitableboron hydrides include, without intended limitation, the group ofborohydride salts [M(BH₄)_(n)], triborohydride salts [M(B₃H₈)_(n)],decahydrodecaborate salts [M₂(B₁₀H₁₀)_(n)], tridecahydrodecaborate salts[M(B₁₀H₁₃)_(n)], dodecahydrododecaborate salts [M₂(B₁₂H₁₂)_(n)], andoctadecahydroicosaborate salts [M₂(B₂₀H₁₈)_(n)], where M is an alkalimetal cation, alkaline earth metal cation, aluminum cation, zinc cation,or ammonium cation, and n is equal to the charge of the cation. For theabove-mentioned boron hydrides, M is preferably sodium, potassium,lithium, or calcium. Suitable borane hydrides also include, withoutintended limitation, neutral borane compounds, such as decaborane(14)(B₁₀H₁₄), tetraborane(10) (B₄H₁₀), and ammonia borane compounds. As usedherein, the term “ammonia boranes” includes compounds containing N—H andB—H bonds such as (a) compounds represented by formula NH_(x)BH_(y),wherein x and y are independently an integer from 1 to 4 and do not haveto be the same, including NH₃BH₃; (b) compounds represented by formulaNH_(x)RBH_(y), wherein x and y are independently an integer from 1 to 4and do not have to be the same, and R is a methyl or ethyl group; (c)NH₃B₃H₇; and (d) dimethylamine borane (NH(CH₃)₂BH₃).

Ionic hydrides include, without intended limitation, zinc hydride andthe hydrides of alkali metals and alkaline earth metals having thegeneral formula MH_(n) wherein M is a cation selected from the groupconsisting of alkali metal cations such as sodium, potassium or lithiumand alkaline earth metal cations such as magnesium or calcium, and n isequal to the charge of the cation. Examples of suitable metal hydrides,without intended limitation, include lithium hydride, sodium hydride,magnesium hydride, calcium hydride, zinc hydride, and the like.

Aluminum hydrides include, for example, alane (AlH₃) and the aluminumhydride salts including, without intended limitation, salts with generalformula M(AlH₄)_(n), where M is an alkali metal cation, alkaline earthmetal cation, aluminum cation, zinc cation, or ammonium cation, and n isequal to the charge of the cation.

Optionally, the boron or other chemical hydride fuel component may becombined with a stabilizer agent selected from the group consisting ofmetal hydroxides, anhydrous metal metaborates, and hydrated metalmetaborates, and mixtures thereof. Solid stabilized fuel compositionscomprising about 20 to about 99.7 wt-% borohydride and about 0.3 toabout 80 wt-% hydroxide salts are disclosed in co-pending U.S. patentapplication Ser. No. 11/068,838 entitled “Borohydride Fuel Compositionand Methods” and filed on Mar. 2, 2005, the disclosure of which isincorporated by reference herein in its entirety.

As used herein, the term “water surrogate” sources means a substancethat when mixed with a chemical hydride and upon warming to atemperature above ambient mimics the hydrogen generation reaction of achemical hydride and water. It is not necessary that free watermolecules be isolated or produced during heating. Water surrogatesources useful in the invention include “proton sources” and “chemicalwater compounds,” which terms are defined below.

As used herein, the term “proton source” means a compound that has atleast one “protic hydrogen” that can be represented as “H⁺”; a protichydrogen is a hydrogen atom bound to an element more electronegativethan hydrogen on the Pauling scale or is bound to Te.

Solid proton sources useful in embodiments of the invention include, forexample, hydroxide salts of alkali and alkaline earth metals; zinchydroxide; alkali metal dihydrogen phosphate salts; alkali metaldihydrogen citrate salts; alcohols; polymeric alcohols; silicates,silica sulfuric acid; acid chloride compounds; hydrogen sulfide; amines;solid state acids with the general formula M_(y)[O_(p)X(OH)_(q)]_(n)where X is S, P, or Se, M is an alkali metal or NH₄, q is an integerfrom 0 to 3, p is an integer from 0 to 3, y is the valence of the anion[O_(p)X(OH)_(q)], and n is the valence of M; sulfate and phosphate saltsof alkali and alkaline earth metals; and hydroxide compounds of Group 13elements. Representative examples of proton sources include, but are notlimited to, boric acid, aluminum hydroxide, lithium hydroxide, sodiumhydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide,sodium dihydrogen phosphate (NaH₂PO₄), Si(OH)₄, Zn(OH)₂, sodiumdihydrogen citrate (C₆H₇NaO₇), polyvinyl alcohol, sodium sulfate, sodiumphosphate, Si(OH)₄, CsHSO₄, CsHSeO₄, and CsH₂PO₄. Representativeexamples of hydrogen storage compositions incorporating proton sourcesare provided in Table 1.

TABLE 1 Compositions wt-% H₂ 2 LiAlH₄ + 1 Al(OH)₃ 6.87 3 LiAlH₄ + 4B(OH)₃ 6.70 2 BH₃NH₃ + 2 LiAlH₄ + 1 Al(OH)₃ 10.67 2 MgH₂ + LiBH₄ +Si(OH)₄ 7.09 2 LiAlH₄ + NaHSO₄ 4.11 2 MgH₂ + 2 NaH + NaH₂PO₄ 3.66 4LiAlH₄ + 6 LiOH 7.16 LiBH₄ + 2 LiNH₂

Preferably, the exothermic hydrogen storage compositions, according toembodiments of the invention, comprise mixtures of chemical hydrideswith hydroxide compounds such as the hydroxide salts of alkali andalkaline earth metals and hydroxide compounds of Group 13 elements.These are combined in an admixture such that there are more hydridichydrogens contributed by the chemical hydrides than protic hydrogenscontributed by the hydroxide compounds (determined on a molar basis) inthe composition. This is generally achieved by providing the chemicalhydride in molar excess relative to the hydroxide compound. Preferredcompositions comprise from about 0 to about 6 moles of an aluminumhydride compound, from about 0 to about 6 moles of a boron hydridecompound, from about 0 to about 4 moles of an ionic hydride compound,and from about 0 to about 1 moles of a hydroxide compound. In somepreferred embodiments, the compositions comprise from about 0 to about 6moles of an aluminum hydride compound, from about 0 to about 60 moles ofan ammonia borane compound, from about 0 to about 180 moles of an ionichydride compound, and from about 0 to about 1 moles of a hydroxidecompound.

The term “chemical water compound” as used herein means a compound,polymer, or salt that generates water equivalents via intramolecular orintermolecular reactions that occur upon warming to a temperaturepreferably above ambient. Chemical water compounds do not containmolecular water in the form of H₂O molecules.

Chemical water compounds useful in the present invention include, forexample, carbohydrates including hexoses, pentoses, and sugar alcohols;borate salts; carboxylic acids; bicarbonate salts; allylic alcohols; andthose compounds provided in U.S. Provisional Application Ser. No.60/907,232, filed Mar. 26, 2007, and U.S. application Ser. No.11/524,446, filed Sep. 21, 2006, the entire disclosures of which areincorporated herein by reference in their entirety. Preferably, chemicalwater compounds include mannitol, sorbitol, myo-insitol, fructose,glucose, disodium tetraborate tetrahydrate (Na₂B₄O₇.4H₂O, orNa₂O.2B₂O₃.4H₂O), sodium metaborate dihydrate (NaB(OH)₄, or ½ Na₂O.½B₂O₃.2H₂O), pinnoite (MgB₂O₄.3H₂O, or MgO.B₂O₃.3H₂O), sodiumbicarbonate, citric acid, and malic acid. Representative examples ofhydrogen storage compositions incorporating chemical water sources areprovided in Table 2.

TABLE 2 Compositions wt-% H₂  3 moles NaBH₄ + 1 mole sorbitol 8.18 12moles LiH + 1 mole fructose 8.78  1 mole NaBH₄ + 1 mole fructose 7.40  3moles LiBH₄ + 1 mole mannitol 9.77

As used herein, “endothermic” means that the composition absorbs heat.Suitable solid endothermic compositions for use in the methods of theinvention include materials and mixtures that are capable of absorbingheat that is released by the exothermic hydrogen storage composition andundergoing a chemical or physical change. In an adiabatic system, it ispreferred that the solid endothermic composition be capable of absorbingmost of the heat that the exothermic hydrogen storage composition iscapable of releasing, though under non-adiabatic conditions, some heatwill be lost to the environment and the endothermic composition need notabsorb all of the heat released by the exothermic hydrogen storagecomposition.

The chemical change undergone by the endothermic composition may be achemical reaction that generates a gas, such as carbon dioxide orhydrogen. Endothermic compositions comprising carbonate compounds, forexample but not limited to MgCO₃, CaCO₃, Na₂CO₃, ZnCO₃, and NaHCO₃, willproduce carbon dioxide when heat is absorbed. An example of this type ofendothermic gas generation composition is shown in the followingEquation:MgCO₃→MgO+CO₂ΔH(300° C.)=−99 kJ  Eqn. 1

Endothermic compositions that include (a) at least one chemical hydridecombined with at least one alkali or alkaline earth metal amide orimide; or (b) at least partially hydrogenated pi-conjugated organicsystems; or (c) metal hydrides, will produce hydrogen gas upon theabsorption of heat. Examples of suitable hydrogen storage compositionsare provided in Table 3, and further described below.

TABLE 3 H₂ Evolution wt. H₂ Temp Range Compound (%) (° C.) LiNH₂ + 2LiH10.4 150-245 LiAlH₄ + 2LiNH₂ 9.6 125-250 2LiAlH₄ + LiNH₂ 10.2 125-250LiBH₄ + 2LiNH₂ 11.9 250-300 Mg(NH₂)₂ + 4LiH 9.2 135-290 MgH₂ + 2LiNH₂8.4 135-190 MgH₂ 7.7 280-300 Mg₂NiH₄ 3.6 280 LaNi₅H₆ 1.4 25Perhydro-Coronene (C₂₄H₃₆)—24H 7.4 169 Perhydro-4,7-phenanthroline(C₁₂N₂H₂₂)—14H 7.2 150-225 Perhydro-N-methylcarbazole (C₁₃NH₂₃)—12H 6.2125-200 Perhydro-N-ethylcarbazole (C₁₄NH₂₅)—12H 5.8 100-200Perhydro-N-methylimidazole (C₄N₂H₁₀)—4H 4.7  60-125

(A) While not wishing to be bound by theory, mixtures of chemicalhydrides and alkali or alkaline earth metal nitrogen hydrogen compounds,such as amides or imides, undergo dehydriding reactions to producehydrogen when heated. These mixtures can comprise equimolar amounts ofchemical hydrides and metal nitrogen hydrogen compounds, or one of themetal nitrogen hydrogen compound or chemical hydride may be present inmolar excess. Preferably, the metal nitrogen hydrogen compound isselected from the group consisting of LiNH₂, NaNH₂, KNH₂, CsNH₂,Mg(NH₂)₂, Ca(NH₂)₂, Li₂NH, Na₂NH, K₂NH, MgNH, and CaNH, and the chemicalhydride is preferably selected from the group of NaBH₄, LiBH₄, KBH₄,MgH₂, LiH, NaH, KH, LiAlH₄, and NaAlH₄. As an example, the reactionbetween lithium amide and lithium hydride occurs as shown in Equation 2to produce hydrogen:LiNH₂+2LiH→Li₃N+2H₂10.4 wt-% H₂,161 kJ overall  Eqn. 2

(B) Methods and compositions suitable for dehydrogenation of at leastpartially hydrogenated analogues of pi-conjugated organic systems toproduce polycyclic aromatic hydrocarbons are disclosed, for example, inU.S. Pat. No. 7,101,530 B2 entitled “Hydrogen Storage by ReversibleHydrogenation of Pi-Conjugated Substrates,” the entire disclosure ofwhich is hereby incorporated herein in its entirety. As an example, twoat least partially hydrogenated analogues of the compound naphthalene(C₁₀H₈) are tetralin (C₁₀H₁₂) and decalin (C₁₀H₈).

Suitable at least partially hydrogenated pi-conjugated organic systemsinclude the perhydrogenated analogues of polycyclic hydrocarbons orpolymeric aromatic hydrocarbons, among others. These fused ringstructures release hydrogen with the absorption of heat to producepi-conjugated molecules such as hexabenzocoronene, polyacenes, rubicene,picene, ovalene, coronene, perylene, pyrene, phenanthrene, anthracene,naphthalene, benzene, indolylmethane, indolocarbazoles,N-alkylcarbazoles, fluorene, indene, and acenaphthylene, and polymerichydrocarbons with heteroatoms including polyfurans, polypyrroles,polyindoles, and polycarbazoles. The at least partially hydrogenatedpi-conjugated organic systems can incorporate one or more heteroatomsselected from the group consisting of nitrogen, oxygen, silicon, boron,sulfur, and phosphorous. Catalysts including, for example, platinum,palladium, rhodium, cobalt, and ruthenium, supported on substrates suchas activated carbon, coke, charcoal, or alumina (Al₂O₃), can be includedwith the at least partially hydrogenated pi-conjugated organic systemsto promote hydrogen production.

(C) Metal hydrides that will release hydrogen upon the application ofheat include compounds such as NaAlH₄, Na₃AlH₆, LiNH₂, MgH₂, LiBH₄—MgH₂mixtures, and AB-, AB₂-, AB₅-, and A₂B-type metal hydrides, includingthe hydrides of metal alloys of titanium, iron, manganese, nickel, andchromium, such as Mg₂Ni, LaNi₅, and FeTi.

Fuel compositions comprising at least one chemical hydride and zinccarbonate basic (the double salt of zinc carbonate and zinc hydroxide in2-to-3 stoichiometric proportion represented by formula 2ZnCO₃.3Zn(OH)₂), can be used in accordance with embodiments of thepresent invention. The combination of the at least one chemical hydrideand the zinc hydroxide will react to produce hydrogen in an exothermicreaction, from which the heat evolved can be transferred to the zinccarbonate salt to produce carbon dioxide in an endothermic reaction.

Exothermic hydrogen storage compositions used in conjunction with solidendothermic compositions in accordance with embodiments of the presentinvention are preferably packaged in a fuel cartridge or other storagedevice. The fuel cartridge can provide hydrogen to a power modulecomprising a fuel cell or hydrogen-burning engine for conversion toenergy, or to a hydrogen storage device such as a hydrogen cylinder, ametal hydride, or a balloon. The fuel cartridge controls hydrogenrelease from the fuel compositions using an array of fuel compartmentsand thermal initiators, in which the fuel compartments are separatedfrom each other.

Referring now to FIG. 1, an exemplary fuel cartridge 100 useful inembodiments of the present invention comprises a plurality of fuelcompartments 110 separated by walls 114 and disposed within a housing120. At least a portion of the fuel compartment's walls 114 are porousand are configured to allow the hydrogen generated within each fuelcompartment to pass into the fuel cartridge while retaining the pre- andpost-reaction solids with the fuel compartment 110. The fuelcompartments can be tubes, or can be formed as compartments within amaterial. As used herein, the term “tube” is not limited to circularforms and structures, and can include, for example, hexagonal tubes orstructures or square tubes or structures among others. Suitablematerials for forming fuel compartments and for the walls 114 includeglass, ceramics, plastics, polymers, aerogels, and xerogels, among manyothers.

The walls 114 may bound the fuel compartments 110 on multiple sides, andcan be located, for instance, on the terminal ends of a row of fuelcompartments, between fuel compartments, or across the top of individualfuel compartments. Preferably, the fuel compartment walls 114 have aporosity of at least 10%, more preferably at least 20%, and mostpreferably at least 50%.

Preferably, the fuel compartments are thermally isolated from each othersuch that the thermal initiation of an exothermic hydrogen generationstorage composition in a first compartment does not cause an exothermichydrogen generation storage composition in a neighboring fuelcompartment to also initiate. Walls 114 may be a thermal insulator ormay conduct some heat as long as their thermal conductivity does notresult in the transfer of enough thermal energy to initiate neighboringfuel compartments.

Each fuel compartment preferably contains at least one exothermichydrogen generation storage composition 102 and at least one endothermiccomposition 202. These compositions are preferably compacted into a formsuch as a pill or a pellet, though other solid forms can be used. Theexothermic composition 102 and the endothermic composition 202 may beformed in separate pills or pellets, or may be combined into a singlepellet. The amount or formulation of the exothermic hydrogen generationstorage composition 102 and endothermic composition 202 in each of thefuel compartments need not be the same, and can be varied, for example,to produce different amounts of hydrogen from different fuelcompartments. The endothermic composition 202 cannot be initiatedindependently of the exothermic hydrogen generation storage composition102, and the initiation element 112 does not directly initiate areaction in the endothermic material 202. The fuel compartments may becompletely filled, or there may be void space within the fuelcompartment.

The exothermic hydrogen generation storage composition 102 within eachfuel compartment is in contact with an initiation element 112 that canbe individually controlled. The relative location of the initiationelement 112 within the fuel compartment is not limited and may belocated anywhere within the fuel compartment as long as it is in contactwith at least a portion of the exothermic hydrogen generation storagecomposition 102. Initiation elements suitable for use in the inventioninclude, but are not limited to, resistance heaters, nickel-chromiumresistance wires, spark ignitors, thermistors, and heat exchangers.

The fuel cartridge can be equipped with an optional hydrogen outlet 116to supply hydrogen to, for example, a hydrogen-consuming orhydrogen-storing device. The cartridge may further include hydrogen flowregulating mechanisms that condition the hydrogen to a desiredtemperature and pressure such as heat exchangers, pressure regulators,and gas scrubbers or filters. In some embodiments, a fuel cell may becontained within the fuel cartridge and the optional hydrogen outlet 116would not be required. Such a cartridge can contain gas conduits withinthe cartridge to provide hydrogen to the anode of the fuel cell. Thefuel cartridges can further contain transducers or other measurementdevices, such as thermocouples or pressure gauges, for example, and canmonitor system parameters including, but not limited to, temperature andpressure.

Referring now to FIG. 2A, wherein features that are similar to thoseshown in previous figures have like numbering, an arrangement of a fuelcompartment according to an exemplary embodiment of the inventionincludes walls 114 bounding a plurality of exothermic hydrogen fuelcompositions 102 (102 a, 102 b, 102 c, and 102 d), preferably formedinto pellets (also referred to as “exo pellets”), separated from eachother by endothermic compositions 202 (202 a, 202 b, 202 c, and 202 d),preferably formed into pellets (also referred to as “endo pellets”),wherein each of the hydrogen fuel compositions 102 is in contact with aseparate initiation element 112 (112 a, 112 b, 112 c, and 112 d). Such adesign is described herein as “stacks and wells,” wherein a plurality ofalternating exothermic compositions 102 and endothermic compositions202, a “stack,” are placed within a single fuel compartment, or “well.”For illustrative purposes only, the stack configuration in FIG. 2comprises four pairs of endothermic and exothermic compositions; thisembodiment is not limited to the illustrated exemplary arrangement.Stacks and wells can be arranged in a variety of geometric arrangementswithin a cartridge.

Spacers can be optionally included within a stack to separate pairs ofendothermic and exothermic compositions. For example, referring to FIG.2B, spacers 130 can be included between endothermic composition 202 aand initiation element 112 b, between endothermic composition 202 b andinitiation element 112 c, and between endothermic composition 202 c andinitiation element 112 d. Preferably, the spacers 130 permit hydrogengas to pass though and are comprised of glass, ceramics, cellulose,minerals, xerogels or aerogels, for example. The spacers can beconfigured as textiles, fabrics, tapes, strips, boards, or papers, amongothers. Examples of useful materials for spacers include, but are notlimited to, boron nitride, high alumina ceramics, zirconium phosphateceramics, alumina bisque, alumina silicate, glass mica, silica, alumina,zirconia, fiberglass, vermiculite-coated fiberglass, mineral-treatedfiberglass, silicone-coated fiberglass, carbon fabric, high aluminafabric, silica fabric, calcium silicate, millboard, chromia, tin oxide,and carbon.

Further, each exo pellet may be bounded on both sides by an endo pelletas illustrated in FIG. 2C, wherein features that are similar to thoseshown in previous figures have like numbering. In such an arrangement,an exothermic composition 102 bounded on both sides by an endothermiccomposition 202 comprises a “unit cell” of the stack and each unit cellcan be further separated from its neighbors by an optional spacer 130.FIG. 2C illustrates two unit cells, a first unit cell represented by theexo pellet 102 a bounded by two endo pellets 202 a and a second unitcell represented by the exo pellet 102 b bounded by two endo pellets 202b. Upon the initiation of a first exo pellet 102, hydrogen and heat arereleased in an exothermic reaction. The heat released from the exopellet can be used to initiate hydrogen generation from both of theneighboring endo pellets.

The endo and exo pellets do not need to be the same size; the size ofeach pellet is instead related to the relative quantity of heat releasedfrom the exo pellet and the quantity of heat absorbed by the endopellet. Referring to FIGS. 3A and 3B, in some exemplary embodiments theendo pellets and exo pellets may be substantially the same size (FIG.3A), the endo pellet can be larger than the exo pellet (FIG. 3B), or theexo pellet may be larger than the endo pellet (not illustrated). Theendo pellet should preferably be sufficiently heat-absorbing such thatadjacent exo pellets do not initiate in response to hydrogen generationand heat release from a first exo pellet. It is not necessary howeverthat the endo pellet absorb all of the heat released by adjacent exopellets. Adjacent exo pellets can be initiated by using an initiationelement 112 that contacts an individual pellet.

The fuel compartments can be arranged in multiple layers as illustratedin FIG. 4, wherein an exothermic hydrogen storage composition 102, forexample, formed as a pellet, in a first layer is juxtaposed to anendothermic composition 202 in an adjacent layer.

In another exemplary embodiment, the at least one exothermic hydrogengeneration storage composition 102 and at least one endothermiccomposition 202 are contained within separate fuel compartments ratherthan stacked within a single compartment. Such compartments may bearranged, for example, in a linear sequential arrangement as shown inFIG. 5, or in nested arrangements such a concentric circles as shown inFIG. 6, or a honeycomb configuration as shown in FIG. 7.

Referring to FIGS. 5 to 7, a plurality of fuel compartments 302configured to retain at least one exothermic hydrogen storagecomposition 102 are bounded by walls 320 and comprise at least oneinitiation element 112 (not illustrated in these figures). Preferably,at least a portion of the walls 320 have a porosity of at least 10%, andmore preferably at least 20%, and most preferably at least 50%, and thewalls 320 are configured to allow the hydrogen generated within eachfuel compartment to pass from the fuel compartment while retaining thesolid and liquid materials with the fuel compartment 302. Preferably,each of the fuel compartments 302 is adjacent to a compartment 304configured to retain an endothermic composition 202. Either a fuelcompartment 302 or an endothermic chamber 304 may comprise the outermostcell of an array of fuel compartments. In certain preferred embodiments,an endothermic compartment 304 comprises the outermost layer.

To assist in the transfer of heat from the exothermic hydrogen storagecomposition 102 in a fuel compartment 302 to an endothermic composition202 in a compartment 304, wall 320 a may comprise a material with highthermal conductivity such as, for example, metal or ceramic foams. Thewall may further comprise heat fins extending into the compartment 304containing the endothermic composition 202.

Hydrogen is generated from the exothermic hydrogen generation storagecomposition when heat is applied, preferably by initiating at least onecompartment at a time. Multiple compartments can be initiated at thesame time to achieve variable hydrogen generation rates or generated gasvolumes. The initiation can be achieved, for example, by heating thecompartment as a whole, or by an initiation element in contact with theexothermic hydrogen generation storage composition. The exothermiccomposition 102 within each fuel compartment is in contact with aninitiation element 112, such as, for example, a resistance heater, aspark igniter, a nickel-chromium resistance wire, or a heat exchanger,that can be individually controlled. The relative location of theinitiation element 112 within the fuel compartment is not limited andmay be located anywhere within the fuel compartment as long as it is incontact with at least a portion of the exothermic hydrogen generationstorage composition 102.

Referring back to FIG. 2, a method for hydrogen generation using a stackand well configuration, comprises operating a first initiation element112 a to initiate a reaction of a first exothermic hydrogen storagecomposition 102 a to produce both heat and hydrogen. This heat isabsorbed by the endothermic composition 202 a resulting in a reaction,such as the generation of additional hydrogen. A second initiationelement 112 b can then initiate a second exothermic hydrogen storagecomposition 102 b to produce heat and hydrogen, and then that heat isabsorbed by a second endothermic composition 202 b. This process can berepeated with a third exothermic hydrogen storage composition 102 c anda fourth exothermic hydrogen storage 102 d composition, and so on, untilall exothermic hydrogen storage compositions 102 within a given fuelcompartment have been reacted. Multiple stacks within a fuel compartment110, and/or multiple fuel compartments, may be operated concurrently orindividually.

Alternatively, a stack can be initiated in an “inside out” process in amethod which includes operating a first initiation element 112 b toinitiate a reaction of a first exothermic hydrogen storage composition102 b to produce both heat and hydrogen. That heat is absorbed by theendothermic composition 202 b resulting in a reaction, such as thegeneration of additional hydrogen. A second initiation element 112 c canthen initiate a reaction of a second exothermic hydrogen storagecomposition 102 c to produce heat and hydrogen, and then that heat isabsorbed by a second endothermic composition 202 c. This process can berepeated with a third exothermic hydrogen storage composition 102 a anda fourth exothermic hydrogen storage 102 d composition and so on, untilall exothermic hydrogen storage compositions 102 within a given fuelcompartment have been reacted.

A “fuel gauge” feature can be incorporated into fuel cartridgesaccording to the disclosed and other embodiments of the presentinvention to indicate the number of compartments—and thus how muchenergy—remains in the device by including a controller to monitor thenumber of compartments which have been heated and used. Each compartmentis typically initiated one time, after which it will not produce anymore hydrogen. Within the control architecture, the controller willmonitor which compartments have been used and which have not, as well asthe total number of compartments, so that it can initiate the nextreaction in the proper place. An exemplary fuel gauge can report acompletion percentage indicating the remaining fuel by computing thenumber of compartments that have been used divided by the total numberof compartments. For example, if the device contains 100 compartments,and 53 have been used, then the cartridge is 53% spent (or has 47% ofits energy remaining).

In reference to the illustrated embodiments, the initiation element 112has been shown as a plate that resides in the stack with the pellets(for example, as shown in FIG. 8A). Other arrangements of initiationelements and exo pellets useful in these and other embodiments of theinvention are presented in FIGS. 8B and 8C. In some embodiments, theinitiation element 112 need only contact a portion of the pellet inorder to initiate a complete reaction. An initiation element 112, suchas a resistance heater, touching the surface of an exo pellet (such asone containing LiAlH₄ and Al(OH)₃ in a 2:1 molar ratio) as shown in FIG.8B, initiates the reaction of the entire pellet. The initiation element112 can alternatively be a wire that is in contact with a face of apellet, as shown in FIG. 8C. Such a wire can be between the endo pelletsand the exo pellets.

In an exemplary embodiment of a hydrogen generation composition, theexothermic hydrogen generation storage composition comprises a mixtureof lithium aluminum hydride (LiAlH₄) and aluminum hydroxide (Al(OH)₃)combined in a molar ratio of about 2 to about 4 moles of LiAlH₄ per moleof Al(OH)₃, and the endothermic composition comprises a mixture oflithium hydride (LiH) and lithium amide (LiNH₂) in a molar ratio ofabout 1 to about 2 moles of LiH per mole of LiNH₂ (Equation 2). TheLiAlH₄/Al(OH)₃ reaction produces 705 kJ utilizing 4 moles of LiAlH₄ and2 moles of Al(OH)₃, which is sufficient energy to raise the reactanttemperature of the endothermic reaction materials (such as the reactantshown in Equation 2) and drive the dehydrogenation of 4 moles of thelithium amide and 8 moles of lithium hydride which requires 161 kJ permole of lithium amide as shown in Equation 2. The net yield of thecoupled reactions is 8.05 wt-% H₂ from the reagents and about 3 kJ ofheat released per mole of H₂ released.

In another exemplary embodiment of a hydrogen generation composition,the exothermic hydrogen generation storage composition comprises amixture of LiH with fructose, and the endothermic composition comprisesthe perhydro-form of coronene. LiH and fructose will react to producehydrogen and heat when thermally intitated, as provided in Equation 3.The heat can be used to drive the dehydrogenation of perhydrocoronene tocoronene (Equation 4).12LiH+C₆H₁₂O₆→6Li₂O+6C+12H₂ΔH=−1319 kJ@300° C.  Eqn. 3C₂₄H₃₆→C₂₄H₁₂+12H₂ΔH=+1296 kJ@300° C.  Eqn. 4

The stoichiometry illustrated in Equation 3 produces 1319 kJ per mole offructose, which is sufficient energy to raise the reactant temperatureof the endothermic reaction materials (e.g., such as the reactant shownin Equation 4) and drive the dehydrogenation of one mole of theperhydro-form of coronene to coronene which requires 1296 kJ per mole ofcoronene as shown in Equation 4. The net yield of the coupled reactionsis 8.06 wt-% H₂ from the reagents and less than 1 kJ of heat releasedper mole of H₂ released.

In another exemplary embodiment of a hydrogen generation composition,the exothermic hydrogen generation storage composition comprises amixture of ammonia borane (BH₃NH₃), lithium aluminum hydride (LiAlH₄),and aluminum hydroxide (Al(OH)₃) combined in a molar ratio of 4:4:2,respectively, and the endothermic composition comprises magnesiumcarbonate (MgCO₃) as described in Equation 1. The thermal initiation ofthe exothermic mixture will produce both hydrogen and heat which in turnwill drive the thermal decomposition of the endothermic component MgCO₃to produce carbon dioxide (Equation 1). The BH₃NH₃/LiAlH₄/Al(OH)₃reaction produces 1202 kJ utilizing 4 moles each of BH₃NH₃ and LiAlH₄,and 2 moles of Al(OH)₃, which is sufficient energy to raise the reactanttemperature of the endothermic reaction materials (such as the reactantshown in Equation 1) and drive the decomposition of 12 moles of theMgCO₃ which requires 99 kJ per mole of magnesium carbonate as shown inEquation 1. The net yield of the coupled reactions is 3.15 wt-% H₂ fromthe reagents and less than 1 kJ of heat released per mole of H₂released.

While the present invention has been described with respect toparticular disclosed embodiments, it should be understood that numerousother embodiments are within the scope of the present invention.Accordingly, it is not intended that the present invention be limited tothe illustrated embodiments, but only by the appended claims.

The invention claimed is:
 1. A system for hydrogen generationcomprising: a plurality of gas generation pairs configured in a stackedarrangement, wherein each gas generation pair comprises a first pelletof an exothermic hydrogen generation composition in contact with asecond pellet of an endothermic gas generation composition; and aninitiation element in contact with each first pellet, wherein theinitiation element is operable to transfer thermal energy to theassociated first pellet sufficient to initiate the exothermic hydrogengeneration composition to undergo an exothermic reaction withoutadditional material; wherein heat released from the exothermic reactioninitiates the endothermic gas generation composition to undergo anendothermic reaction and sustains the exothermic reaction and theendothermic reaction to release hydrogen.
 2. The system of claim 1,wherein each gas generation pair further comprises an initiation elementin contact with the first pellet of the exothermic hydrogen generationcomposition.
 3. The system of claim 1, wherein the gas generation pairfurther includes a third pellet of an endothermic gas generationcomposition in contact with the first pellet of the exothermic hydrogengeneration composition.
 4. The system of claim 1, further comprising aspacer between the gas generation pairs.
 5. The system of claim 4,wherein the spacer is configured to permit hydrogen gas to passtherethrough.
 6. The system of claim 4, wherein the spacer is comprisedof a material selected from the group consisting of glass, ceramics,cellulose, minerals, xerogels and aerogels.
 7. The system of claim 1,wherein the first pellet of the exothermic hydrogen generationcomposition and the second pellet of the endothermic gas generationcomposition have the same size.
 8. The system of claim 1, wherein thefirst pellet of the exothermic hydrogen generation composition and thesecond pellet of the endothermic gas generation composition havedifferent sizes.
 9. The system of claim 1, wherein the endothermic gasgeneration composition comprises a mixture of at least one chemicalhydride and at least one metal nitrogen hydrogen compound.
 10. Thesystem of claim 9, wherein the chemical hydride is selected from thegroup consisting of NaBH₄, LiBH₄, KBH₄, MgH₂, LiH, NaH, KH, LiAlH₄, andNaAlH₄.
 11. The system of claim 9, wherein the at least one metalnitrogen hydrogen compound is selected from the group of alkali andalkaline earth metal amides and imides consisting of LiNH₂, NaNH₂, KNH₂,CsNH₂, Mg(NH₂)₂, Ca(NH₂)₂, Li₂NH, Na₂NH, K₂NH, MgNH, and CaNH.
 12. Thesystem of claim 9, wherein the mixture comprises LiH and LiNH₂ combinedin a molar ratio of about 2:1.
 13. The system of claim 9, wherein themixture comprises LiAlH₄ and LiNH₂ combined in a molar ratio of about2:1.
 14. The system of claim 9, wherein the mixture comprises LiAlH andLiNH₂ combined in a molar ratio of about 1:2.
 15. The system of claim 9,wherein the mixture comprises MgH₂ and LiNH₂ combined in a molar ratioof about 1:2.
 16. The system of claim 9, wherein the mixture comprisesLiH and Mg(NH₂)₂ combined in a molar ratio of about 4:1.
 17. The systemof claim 1, wherein the endothermic gas generation composition comprisesan at least partially hydrogenated pi-conjugated organic system.
 18. Thesystem of claim 17, wherein the at least partially hydrogenatedpi-conjugated organic system is selected from the group consisting ofhexabenzocoronene, rubicene, picene, ovalene, coronene, perylene,pyrene, phenanthrene, and anthracene.
 19. The system of claim 17,wherein the at least partially hydrogenated pi-conjugated organic systemis selected from the group consisting of indolylmethane,indolocarbazoles, N-alkylcarbozoles, fluorene, indene, acenaphthylene,polyfurans, polypyrroles, polyindoles, and polycarbazoles.
 20. Thesystem of claim 1, wherein the endothermic gas generation compositioncomprises a metal hydride.
 21. The system of claim 20, wherein the metalhydride is selected from the group consisting of NaAlH₄, Na₃AlH₆, LiNH₂,MgH₂, LaNi₅, and mixtures of LiBH₄—MgH₂.
 22. The system of claim 20,wherein the metal hydride is selected from the group consisting of AB-,AB₂-, AB₅-, and A₂B-type metal hydrides and the hydrides of metal alloysof titanium, iron, manganese, nickel, and chromium.
 23. The system ofclaim 20, wherein the metal hydride is Mg₂Ni, LaN is, or FeTi.
 24. Thesystem of claim 1, wherein the endothermic gas generation compositioncomprises a carbonate compound.
 25. The system of claim 24, wherein thecarbonate compound is magnesium carbonate.
 26. The system of claim 1,wherein the exothermic gas generation composition comprises a mixture ofat least one chemical hydride and at least one water surrogate source.27. The system of claim 26, wherein the at least one chemical hydride isselected from the group consisting of boron hydrides, ionic hydridesalts, and aluminum hydrides.
 28. The system of claim 26, wherein the atleast one chemical hydride is a boron hydride selected from the groupconsisting of borohydride salts [M(BH₄)_(n)], triborohydride salts[M(B₃H₈)_(n)], decahydrodecaborate salts [M₂(B₁₀H₁₀)_(n)],tridecahydrodecaborate salts [M(B₁₀H₁₃)_(n)], dodecahydrododecaboratesalts [M₂(B₁₂H₁₂)_(n)], and octadecahydroicosaborate salts[M₂(B₂₀H₁₈)_(n)], where M is an alkali metal cation, alkaline earthmetal cation, aluminum cation, zinc cation, or ammonium cation, and n isequal to the charge of the cation.
 29. The system of claim 26, whereinthe at least one chemical hydride is a boron hydride selected from thegroup consisting of decaborane (14) (B₁₀H₁₄) and tetraborane (10)(B₄H₁₀).
 30. The system of claim 26, wherein the at least one chemicalhydride is an ammonia borane selected from the group consisting ofcompounds of formula NH_(x)BH_(y) and NH_(x)RBH_(y), wherein x and y areindependently an integer from 1 to 4 and do not have to be the same, andR is a methyl or ethyl group; NH₃B₃H₇, and NH(CH₃)₂BH₃.
 31. The systemof claim 26, wherein the at least one chemical hydride is an ionichydride selected from the group consisting of hydrides of alkali metals,alkaline earth metals, and zinc metal having the general formula MHnwherein M is a cation selected from the group consisting of alkali metalcations, alkaline earth metal cations, and zinc(II), and n is equal tothe charge of the cation.
 32. The system of claim 26, wherein the atleast one chemical hydride is an aluminum hydride selected from thegroup consisting of alane and aluminum hydride salts.
 33. The system ofclaim 32, wherein the aluminum hydride salts have the formulaM(AlH₄)_(n), where M is an alkali metal cation, alkaline earth metalcation, aluminum cation, zinc cation, or ammonium cation, and n is equalto the charge of the cation.
 34. The system of claim 26, wherein the atleast one water surrogate source is selected from the group consistingof hydroxide salts of alkali and alkaline earth metals, and hydroxidecompounds of Group 13 elements.
 35. The system of claim 26, wherein theat least one water surrogate source is selected from the groupconsisting of alkali metal dihydrogen phosphate salts; alkali metaldihydrogen citrate salts; sulfate salts of alkali and alkaline earthmetals, phosphate salts of alkali and alkaline earth metals; andcompounds of formula M_(y)[O_(p)X(OH)_(q)]_(n) where M is an alkalimetal or NH4, q is an integer from 0 to 3, p is an integer from 0 to 3,y is the valence of the anion [O_(p)X(OH)_(q)], and n is the valence ofM, and X is S, P, or Se.
 36. The system of claim 26, wherein the atleast one water surrogate source is selected from the group consistingof alcohols; polymeric alcohols; silicates; silica sulfuric acid; acidchloride compounds; hydrogen sulfide; and amines.
 37. The system ofclaim 26, wherein the at least one water surrogate source is selectedfrom the group consisting of carbohydrates; borate salts; carboxylicacids; bicarbonate salts; and allylic alcohols.